The present invention relates to stable aqueous colloidal dipersions of sulfopolyureas and self supporting films formed from the dispersions which display good mechanical properties from about room temperature to temperatures exceeding 150.degree. C. The films of the invention, which are formed with no volatile organic compound (VOC) emissions and no post-coating chemical or ionic cross-linking, are not redispersible in water and may be used to form heat resistant abrasive articles.
Polyurethanes are a well established class of high performance polymers which can be readily tailored to display a unique combination of tensile strength, toughness, and flexibility. As a result of this versatility, polyurethanes have found utility in a variety of applications including binder resins, abrasion resistant coatings, protective coatings, and membranes.
Polyurethanes may be delivered to a substrate as a thermoplastic or thermoset material by an extrusion process, as a moisture cure or two part curable system, generally from an organic solvent, or as an aqueous dispersion of a colloidal polymer system. Two part polyurethanes are generally used in binder or coating applications where they are delivered from mixtures of organic solvents, blocked isocyanate terminated compounds, and polyols, or mixtures of organic solvents, a diisocyanate terminated compound, and polyols.
Aqueous polyurethane dispersions have been developed as a means to deliver polyurethane coatings to substrates such as fibers, textiles, and paper. They offer advantages over two part polyurethane systems in that they have reduced volatile organic compound (VOC) emissions, they may eliminate exposure to toxic isocyanate or diamine compounds during coating, and they provide simplified overall processing.
Attempts to improve the thermal stability and flow resistance properties of aqueous polyurethane materials by incorporation of crosslinking monomers which react with the polyurethane backbone (e.g. epoxy resins) have been only partially successful. Improved high temperature performance has typically been achieved at the expense of reduced toughness and elongation, and dramatically increased modulus.